Electronic devices may be damaged if supplied with voltages that are higher than a design limit or that have an incorrect polarity. The supplying of such improper voltages may occur for a number of reasons.
For example, the Universal Serial Bus (USB) standard has been updated to permit the provisioning of either 5, 12, or 20 volt supply voltages to USB devices. Whether to provides 5, 12, or 20 volts is determined according to a negotiation between the USB device supplying the power and the USB device receiving the power.
The USB standard has also been updated to include connectors that have a finer contact pitch. As a result, shorting or misalignments may occur. This may cause the supply voltage to be delivered to a ground terminal of the USB device and vice-versa, reversing the polarity of the supply voltage from the perspective of the USB device receiving it.
If the voltage negotiation process malfunctions or a defect exists in the connection between the USB device supplying the power and the USB device receiving the power, one or both USB devices may be damaged. For example, a USB device designed to operate from 5 volts may be damaged upon receiving 20 volts, −5 volts, or −20 volts on its power supply input.
Accordingly, it is desirable to have circuits and methods for protecting devices from voltage above a design value and from voltages having improper polarities.
Those skilled in the field of the present disclosure will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments. This avoids obscuring the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures herein. The details of well-known elements, structures, or processes that are necessary to practice the embodiments and that are well known to those of skill in the art may not be shown and should be assumed present unless otherwise indicated.